The water cavity model of engine’s cylinder head is reconstructed by CAD through slicing method. The reverse design methods which are used for complex interior structure’s surface are explored based on slicing method and using software such as Imageware and UG, through modeling the water cavity. The technologies of reverse design such as the measure method of points cloud, points cloud data treatment, curve fitting, fitting error analysis, surface reconstructive and solid modeling are studied. The reverse methods for complex surface are put forward which are based on blocks and features of model. Through the practice of reversing design for cylinder head water cavity model, it is proven that the complex inner cavity components can be reversed by slicing method. The methods can be referenced for similar reverse design.